Apparatus for detecting defects in needles

ABSTRACT

An apparatus for detecting faulty needles on an operating loom, particularly an operating hosiery loom. The apparatus comprises at least one magnetic detector, for example a Hall effect probe, mounted so that the needles of the loom pass successively in front of it during operation of the loom, and an associated electronic circuit for receiving signals from the or each detector, identifying those signals indicative of a defective needle, and providing a control signal for stopping the loom when such a signal is identified.

United States Patent [191 Raisin et al.

[4 1 Sept. 16, 1975 1 1 APPARATUS FOR DETECTING DEFECTS IN NEEDLES [75]lnventors: Jean-Pierre Raisin, Troyes; Bernard Helffer, Saint Andre lesVergers, bothof France [73] Assignee: Centre Technique Industriel dit:

Institut Textile de France, Boulogne sur Seine, France [22] Filed: June13, 1974 [21] Appl. N0.: 479,119

5/1972 MCAnhUrMQ. ..66/157 1/1974 Brose ..66/157 Primary Examiner-LouisK. Rimrodt Attorney, Agent, or FirmLewis H. Eslinger; Alvin Sinderbrand[5 7] ABSTRACT An apparatus for detecting faulty needles on an operatingloom, particularly an operating hosiery loom. The apparatus comprises atleast one magnetic detector, for example a Hall effect probe, mounted sothat the needles of the loom pass successively in front of it duringoperation of the loom, and an associated electronic circuit forreceiving signals from the or each detector, identifying those signalsindicative of a defective needle, and providing a control signal forstopping the loom when such a signal is identified.

9 Claims, 2 Drawing Figures 5'6 79b 96 if 12 M Ma 18 20 39 I7PATENTULSEP em 3 905.211

SHEET 1 [IF 2 PATENTEU SEP 1 61975 sum 2 05 2 mw mm mm APPARATUS FORDETECTING DEFECTS IN NEEDLES The present invention relates to anapparatus for detecting defects in needles and relates more particularlyto an apparatus which can detect defects in the needles of a hosieryloom throughout the entire operation of such a loom.

During knitting operations, the latch needles used on hosiery looms maydeteriorate so that they are put out of use or damaged such that theknitted article produced comprises faults.

All hosiery looms at present in use are provided with inspectiondevices. These devices, which are very old, are generally mechanicalfeelers. They are able to detect needles whose latches are closed andadditional thicknesses of knitting which form between the needle rows.in order to operate efficiently, it is necessary that these devices areregulated in an extremely accurate manner, which is generally difficultto carry out. Furthermore, they are unable to detect a needle whose hookis broken.

More recently, optical detectors have appeared. These detectors aresensitive only to the absence of a hook and thus may only be used tocomplement mechanical feelers. The operation of the electronic apparatusassociated with these optical detectors and intended to detect thisabsence is based on the charging of a capacitor in the absence of asignal.

Still more recently. apparatus has appeared for detecting faulty needleson an operating hosiery loom, comprising at least one magnetic detectorarranged such that all the needles pass in succession in front of thelatter during their operating movement. An associated electronic circuitcapable of transforming the signals received from said magnetic detectoris provided which upon detection of a defect of a needle supplies asignal for controlling the stoppage of the loom.

These known magnetic detection devices have the drawback that themagnetic detectors used are constituted only by windings sensitive tothe effect of induction. The low detection power, i.e., the lowsensitivity of such detectors, necessitates the provision of anadditional amplification stage before using the signals emitted by saiddetectors, and the location of the detectors as close as possible to thetrajectory of passage of the needles, in other words at a distance lessthan approximately one-tenth mm. This distance is naturally difficult tomaintain constantly along the entire length of passage of the variousneedles of the loom in front of the detectors.

Furthermore, even if the associated electronic circuits enable thedetection of absences of signal owing to faults, such as the absence ofa needle or a broken hook, they nevertheless do not enable the detectionof signals having an amplitude greater than normal, such as those causedby the opening of the hook, the twisting of the needle towards thefront, or the closure of the latch.

It is thus an object of the present invention to provide an apparatuswhich is capable of detecting practically all types of defects in theneedles of a hosiery loom.

According to the present invention, there is provided an apparatus fordetecting faulty needles on an operating loom, comprising at least onemagnetic detector mounted in use so that the needles of the loom passsuccessively in front of it during operation of the loom,

and an associated electronic circuit for receiving signals from the oreach detector, identifying those signals indicative of a defectiveneedle, and providing a con trol signal for stopping the loom when sucha signal is identified.

The magnetic detectors may be the detectors which are sold under thename of Hall effect probes, which detect and measure variations in themagnetic field caused in their vicinity by the passage of a needle.Other types of magnetic detectors may be used however, such asmagneto-resistance detectors. These two types of detectors, Hall effectprobes and magnetoresistance detectors, comprise thin rectangular platesof semi-conducting material. When Hall effect probes are subject to amagnetic field and traversed by a current at right-angles to said field,a voltage depending on said field and called a Hall voltage is producedbetween two electrodes located at right-angles to the direction of saidcurrent and to that of said magnetic field. Magneto-resistance detectorshave a variable internal resistance depending on the magnetic fieldapplied at right-angles to their major side.

Since these two types of detectors have a sensitivity of co-efficient ofapplication which is much greater than that of conventional detectorscomprising windings, their use makes it possible firstly to eliminatethe previously indispensable amplifier stage and secondly to arrangethem much further away from the trajectory of the needles, for exampleat a distance of several millimetres. In addition, the mounting of suchdetectors on existing machines is simplified in view of theirminiaturization (dimensions: approximately 2mm 1mm X 1/10 mm).

The electronic circuit preferably comprises first and second circuitsarranged in parallel, the first circuit comprising a first comparatorfor detecting faults which cause the appearance of a signal of anamplitude greater than normal and the second circuit comprising a secondcomparator and two monostables connected in series for detecting defectswhich cause the absence of a signal, the first comprator and the secondmonostable being connected to an OR gate which controls a delay triggerfor providing a prolonged control signal for stopping the loom. Thefirst comparator may comprise any equivalent system, for example aSchmitt trigger.

Finally, the connection of several of the detectors in a bridge makes itpossible to eliminate background noise as well as various drawbacks suchas interference and variations of an unpredictable nature which may beproduced in all electronic components.

The signals emitted by the magnetic detectors during the passage of aneedle in their immediate vicinity have very different characteristicsdepending on whether the needle is or is not defective, and theelectronic circuit makes it possible to ensure the detection of a signalcorresponding to any particular defect as soon as it appears, and tostop the loom immediately.

The apparatus of the present invention has the considerable advantageover optical systems of being completely insensitive to dust or powderymaterial which may be located in the vicinity of the needles.

An embodiment of the present invention will now be described, by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 illustrates various types of defects which may occur in theneedles of hosiery looms; and

FIG. 2 is a basic diagram of an apparatus according to the invention.

As shown in FIG. 1 the various defects which may occur in the heads oflatch needles for hosiery looms, such a needle being shown in its normalform at 1 and comprising a hook 1a and a latch 11), may be regrouped infive major categories.

Each of these categories is symbolized by one of the five needlesnumbered 2 to 6, which illustrate the various defects encountered in adiagrammatic form.

Thus, the needle shown at 2 has a broken hook; the needle shown at 3 hasan opened hook 3a, the needle shown at 4 has a broken latch 4b; theneedle shown at 5 has a front part 50 which has been twisted; and theneedle shown at 6 has a closed latch 6b.

Referring now to FIG. 2, the illustrated apparatus comprises a magneticdetector and an associated electronic circuit.

The magnetic detector is composed of two known magnetic detectors 7 soldunder the name of Hall effect probes. A half-bridge connection of theseprobes has been adopted in this case, but other types of connection arenaturally possible, for example a single probe or four probes connectedas a bridge.

Each of the two Hall effect probes 7 is connected in series with aresistance 8 connected to earth 9.

The two probes 7 are supplied in a manner known per se at a constantvoltage by a conventional stabilized supply 10 which is not shown.

The active surface of each probe has a width less than the depth of theneedles to be detected. This width will be less than 50/100 mm. forlooms of English gauge, equal to at the maximum for example, and shouldbe less for looms of finer gauge.

Each magnetic detector is located in the path of the needle hooks at apoint where the latter are located outside the range of any otherferrous member or member having magnetic properties. It is able toinspect the needles during their operating movement to form the stitch,or even during a first displacement prior to said movement. It may bemounted on an inspection door to which is fixed a cam ensuring, in thiscase, the partial ascent of all the needles, whatever their type ifneedles having different lengths or heels of different heights are used.

The electronic circuit is composed of two separate parts each assignedto the detection of certain of the types of defects described.

During the passage of the hook of a normal needle 1 in front of themagnetic detector, the detector emits a pseudo-sinusoidal signal 11 ofgiven amplitude. If the needle which passes in front of the detector hasone of the defects 3 (open hook), 5 (needle twisted at the front) or 6(latch closed), then the detector is influenced by the modification ofthe resulting magnetic field surrounding it which is different from thenormal, and due to this emits a pseudo-sinusoidal signal 12 of anampltude clearly greater than that of the normal signal 11.

If the needle passing in front of the detector has the defect 2 (brokenhook), the absence of the hook results in the magnetic field surroundingthe detector being unmodified, and the detector emits no clear signal asshown at 13.

Finally, if the needle which passes in front of the detector has thedefect 3 (broken latch), the needle is no longer able to knock-down thestitches which it collects. This results in an accumulation of stitcheson its body, which causes the neighbouring needles to move forwards.During their forwards movement, these needles act on the detector liketwisted needles (defect 5 and are consequently detected as describedabove.

Thus, all the above-mentioned defects are detected by the detector andidentified either by the absence of a signal or the presence of a signalof too great an amplitude. Thus, the function of the associatedelectronic circuit is to detect these two types of irregularities andbring about the immediate stoppage of the loom if necessary. A firstpart of the electronic circuit, which carries out the detection ofsignals of too great an amplitude, comprises an electronic comparator14. The comparator 14 receives the signals emitted by one of the Halleffect probes 7 of the magnetic detector at one of its two inputs 14avia a wire 15 which is connected to a wire 16 which joins the respectiveHall effect probe 7 and series resistance 8.

The other input 14b of the electronic comparator 14 is connected by aconnection 40 to a source of reference voltage 17. Thus, each time thecomparator 14 re ceives a signal whose amplitude exceeds a thresholdvalue regulated by the source 17, it emits a pulse 18.

This pulse is applied to an input 19a of an OR gate 19 by means of awire 20 connected to the output 14c of the comparator 14.

The second part of the electronic circuit, which detects the absence ofsignals emitted by the magnetic detector, comprises a second electroniccomparator 21, a first monostable 22 and a second monostable 23connected in series. The monostable 23 is retriggerable so that itsoutput may be held in its unstable state by a series of trigger pulses.

The second electronic comparator 21 has two inputs 21a, 21b connected bywires 25a, 25b to respective ones of the wires 16 which connect the Halleffect probes to their series resistances 8.

Thus, the second electronic comparator 21 continuously receives all theoutputs of the magnetic detectors 7, including the normal signals 11,the signals of increased amplitude 12, and the null signals indicated at13.

The electronic comparator 21 transforms the pseudo-sinusoidal signals 11 and 12, whose amplitudes vary, into square wave signals 24 of constantamplitude.

The first monostable 22, whose input 22a is connected by a wire 25 tothe output 210 of the comparator 21, transforms the sequence of signals24 into a train of pulses 26 of constant width, i.e., duration 26a andof the order of l millisecond. The frequency of these pulses 26 thusdepends on the speed of the loom, since it is dependant upon the passageof the needles in front of the magnetic detectors.

The absence of a signal such as is indicated at 13 results in thesequence of signals 24 being broken by a gap as shown at 27 in FIG. 2,and by a break in the pulse train as shown diagrammatically at 28.

The retriggerable monostable 23 produces a pulse 29 when, at the end ofa predetermined interval, a pulse has not been received at its input23a. This time depends firstly on the adjustment of a R-C networkcomprising a capacitor 30 whose two terminals 30a and 30b are eachconnected to one of two other inputs 23b and 230 of the monostable 23and an adjustable resistance 31 connected between one of the terminals30b of the capacitor 30 and an electronic control member 32, and

secondly on the voltage applied to the adjustable resistance 31 by thecontrol member 32. Since the frequency and consequently the period ofthe pulses is, as has been seen, dependent on the speed of the loom, itis necessary to vary the triggering time of the monostable 23. This isachieved by applying a voltage depending on the loom speed to the R-Cnetwork. This speeddependant voltage is obtained from pulses leaving thefirst monostable by means of the electronic control member whose input32a is connected by a connection 33 to the output 22b of the firstmonostable and whose output 32b is connected by a connection 34 to theadjustable resistance 31 of the R-C network. Thus, since the triggeringtime of the monostable 23 is controlled by the speed of the loom, thedetection of a break in the pulse train is independent of the speed ofthe loom. When a break in the pulse train occurs, the monostable 23provides a pulse 29 on an output 23d of the monostable 23, which outputis connected by a wire 35 to the second input 19b of the OR gate 19.

The capacitor 30 controlling the monostable 23 may be charged by acurrent obtained by any means so as to satisfy the desired conditions asregards its variations depending on the speed of the loom.

The OR" gate 19 thus receives pulses either from the first or from thesecond part of the electronic circuit and in both cases transmits apulse 36 to a delay trigger 37 whose input 37a is connected by a wire 38to the output 190 of said OR gate.

The function of this delay trigger 37 is to extend the output signal ofthe gate in order for it to have a sufficient duration to actuate loomstopping means (not shown), the necessary power being obtained by a meanpower amplifier 39.

We claim:

1. An apparatus for detecting faulty needles on an operating loom,comprising:

magnetic detecting means mounted so that the needles of the loom passsuccessively in front of it during operation of the loom, for producingsignals of a normal amplitude when non-defective needles pass in frontof it, signals of greater than normal amplitude when a first class ofdefective needles pass in front of it and signals of smaller than normalamplitude when a second class of defective needles pass in front of it;

a first electronic circuit connected to said magnetic detecting meansfor identifying signals of greater than normal amplitude indicative of adefective needle, and for providing a first control signal for stoppingthe loom when said defective needle is detected; and

a second electronic circuit connected to said magnetic detecting meansfor identifying signals of smaller than normal amplitude indicative of adefective needle, and for providing a second control signal for stoppingthe loom when said defective needle is detected, said second electroniccircuit comprising means for producing a first output signal in responseto signals which are not of smaller than normal amplitude, and forproducing a second output signal in response to the absence of signalswhich are not of smaller than normal amplitude, during a time intervaldependent on the operating speed of the loom.

2. An apparatus according to claim 1, wherein said first electroniccircuit comprises a first comparator circuit having a first inputconnected to said magnetic detecting means and a second input connectedto a source of reference voltage.

3. An apparatus according to claim 2 wherein said first comparatorcircuit includes a Schmitt trigger.

4. An apparatus according to claim 1 wherein said second electroniccircuit comprises a second comparator circuit for producing first pulseshaving a recurrent frequency equal to the frequency of said signalswhich are not of smaller than normal amplitude, and monostable circuitmeans having a first input connected to said second comparator circuitand a second input connected to electronic control means, saidmonostable circuit means being retriggerable and said electronic controlmeans supplying a voltage dependent on the speed of operation of theloom to said monostable circuit means for making the triggering time ofsaid monostable circuit means dependent on the speed of operation of theloom.

5. An apparatus according to claim 4 wherein said second electroniccircuit further comprises second monostable circuit means responsive tosaid first pulses for producing second pulses having a recurrentfrequency equal to the frequency of said first pulses and havingconstant amplitude and time-width, said second pulses being supplied tosaid electronic control means.

6. An apparatus according to claim 1 further comprising an OR gatehaving a first input connected to said first electronic circuit forreceiving said first control signal, a second input connected to saidsecond electronic circuit for receiving said second control signal andan output connected to an output circuit for producing a control signalof at least predetermined duration for stopping the loom.

7. An apparatus according to claim 1 wherein said magnetic detectingmeans includes at least a Hall effect probe, the active surface of whichhas a width less than the depth of the needles to be detected.

8. An apparatus according to claim 7 wherein said magnetic detectingmeans includes a plurality of Hall effect probes connected as a bridge.

9. An apparatus according to claim 1 wherein said magnetic detectingmeans includes at least a magnetoresistance detector the active surfaceof which has a width less than the depth of the needles to be detected.

1. An apparatus for detecting faulty needles on an operating loom,comprising: magnetic detecting means mounted so that the needles of theloom pass successively in front of it during operation of the loom, forproducing signals of a normal amplitude when non-defective needles passin front of it, signals of greater than normal amplitude when a firstclass of defective needles pass in front of it and signals of smallerthan normal amplitude when a second class of defective needles pass infront of it; a first electronic circuit connected to said magneticdetecting means for identifying signals of greater than normal amplitudeindicative of a defective needle, and for providing a first controlsignal for stopping the loom when said defective needle is detected; anda second electronic circuit connected to said magnetic detecting meansfor identifying signals of smaller than normal amplitude indicative of adefective needle, and for providing a second control signal for stoppingthe loom when said defective needle is detected, said second electroniccircuit comprising means for producing a first output signal in responseto signals which are not of smaller than normal amplitude, and forproducing a second output signal in response to the absence of signalswhich are not of smaller than normal amplitude, during a time intervaldependent on the operating speed of the loom.
 2. An apparatus accordingto claim 1, wherein said first electronic circuit comprises a firstcomparator circuit having a first input connected to said magneticdetecting means and a second input connected to a source of referencevoltage.
 3. An apparatus according to claim 2 wherein said firstcomparator circuit includes a Schmitt trigger.
 4. An apparatus accordingto claim 1 wherein said second electronic circuit comprises a secondcomparator circuit for producing first pulses having a recurrentfrequency equal to the frequency of said signals which are not ofsmaller than normal amplitude, and monostable circuit means having afirst input connected to said second comparator circuit and a secondinput connected to electronic control means, said monostable circuitmeans being retriggerable and said electronic control means supplying avoltage dependent on the speed of operation of the loom to saidmonostable circuit means for making the triggering time of saidmonostable circuit means dependent on the speed of operation of theloom.
 5. An apparatus according to claim 4 wherein said secondelectronic circuit further comprises second monostable circuit meansresponsive to said first pulses for producing second pulses having arecurrent frequency equal to the frequency of said first pulses andhaving constant amplitude and time-width, said second pulses beingsupplied to said electronic control means.
 6. An apparatus according toclaim 1 further comprising an ''''OR'''' gate having a first inputconnected to said first electronic circuit for receiving said firstcontrol signal, a second input connected to said second electroniccircuit for receiving said second control signal and an output connectedto an output circuit for producing a control signal of at leastpredetermined duration for stopping the loom.
 7. An apparatus accordingto claim 1 wherein said magnetic detecting means includes at least aHall effect probe, the active surface of which has a width less than thedepth of the needles to be detected.
 8. An apparatus according to claim7 wherein said magnetic detecting means includes a plurality of Halleffect probes connected as a bridge.
 9. An apparatus according to claim1 wherein said magnetic detecting means includes at least amagneto-resistance detector the active surface of which has a width lessthan the depth of the needles to be detected.